Characterization of the Zirconium Metal-Organic Framework (MOF) UiO-66-NH₂ for the Decomposition of Nerve Agents in Solid-State Conditions Using Phosphorus-31 Solid State-Magic Angle Spinning Nuclear Magnetic Resonance (³¹P SS-MAS NMR) and Gas Chromatography – Mass Spectrometry (GC-MS)

Abstract

UiO-66-NH₂ was synthesized in situ and analyzed as a reactive sorbent for nerve agent removal in the solid-state environment. UiO-66-NH₂ had the smallest pore sizes, centered at 7 Å with added pores at 13 and 15 Å, indicating a hierarchically microporous structure. The in situ reaction was examined using phosphorus-31 solid state-magic angle spinning nuclear magnetic resonance (³¹P SS-MAS NMR) and further confirmed by gas chromatography – mass spectrometry (GC-MS). The results show that the nerve agents were decomposed via hydrolysis by UiO-66-NH₂ and the overall rates were reduced for solid-phase reactions. Of the characterized components O-pinacolyl methylphosphonofluoridate (GD), N, N-dimethylphosphoramidocyanidate (GA), and O-ethyl S-diisopropylaminomethyl methylphosphonothioate (VX), GD was decomposed faster than GA and VX by UiO-66-NH₂. Specifically, GD was decomposed to O-pinacolyl-methylphosphonic acid (PMPA) with a half-life of approximately 430 min in the presence of neat UiO-66-NH₂. However, GA and VX were slowly hydrolyzed, forming reaction products such as ethylphosphate and dimethylphosphoramidic (DMPA) acid monoethylester from GA, and ethyl methylphosphonic acid (EMPA), methylphosphonic acid (MPA), and 2-(Diisopropylamino)ethyldisulfide (DES)₂ from VX, respectively. This work describes the processes involved for these materials when they are deployed to protect against a nerve agent release, implying the practical application of UiO-66-NH₂ for a broad range of filtration applications in the field.

Keywords:

• N
• N-dimethylphosphoramidocyanidate (GA)
• O-ethyl S-diisopropylaminomethyl methylphosphonothioate (VX)
• O-pinacolyl methylphosphonofluoridate (GD) gas chromatography – mass spectrometry (GC-MS)
• phosphorus-31 solid state-magic angle spinning nuclear magnetic resonance (31P SS-MAS NMR)
• zirconium metal organic framework (MOF) UiO-66-NH2N

Acknowledgments

We are thankful to the Chemical Analysis Test and Research Lab at ADD for providing the nerve agents (GD, GA, and VX). We are also grateful to Yungyeong Cho for assisting with the ³¹P SS-MAS NMR experiments. This work was supported by the ADD research project (No. 912762101).